Identification of a melanocyte-type promoter of the microphthalmia-associated transcription factor gene.

Microphthalmia-associated transcription factor (MITF), the human homolog of the mouse microphthalmia gene product, regulates melanocyte-specific transcription of the tyrosinase gene that codes for an essential enzyme in melanin biosynthesis. In this study, we have cloned and characterized the human genomic DNA segment containing a melanocyte-type exon and its 5'-flanking region of the MITF gene. A major transcriptional initiation site was assigned by primer extension and S1 nuclease mapping analyses using melanoma RNA. Subsequently, the fusion genes, containing the identified 5'-flanking region upstream from the firefly luciferase gene, were constructed and were introduced into pigmented melanoma cells or HeLa cells which do not express MITF mRNA. Transient expression assays show that the 5'-flanking region of 2.3 kb is able to confer preferential expression of a luciferase gene in pigment cells. These results establish that the MITF gene contains a melanocyte-specific promoter.